Organs are a system of tissues and cells that perform specific tasks, such as ridding the body of waste, for instance, or respiration.
Our organs are designed with a capacity that is higher than necessary. A 20-year-old's heart, for instance, can pump 10 times more blood than is necessary. However, as we age, the reserve capacity of our organs diminishes - especially in our heart, lungs and kidneys.
Organ donation may occur because genetics or disease may destroy a specific organ, while the rest of our body remains generally healthy.
Other life-sustaining measures, short of organ transplantation, can be used to help diminishing organs. For instance, dialysis can help someone with damaged kidneys. However, dialysis can have a negative effect on other parts of the body. Someone on dialysis has a higher risk of cardiovascular disease because dialysis can reduce antioxidants, which normally fight toxins within the body.
Frequently, the best answer - or perhaps the only answer - is to replace a damaged organ with a healthy one. However, finding healthy organs is not so simple.